The present invention relates to the manufacture of reformed coal and of coke, and more especially to a process for manufacturing the coke with a higher strength and a lower impurity content using the reformed coal and to the products thereof.
It is well known that the properties of coke are determined by the properties of the particular types of coal employed and the ratio in which they are blended when producing coke in a conventional coke oven. In order to produce coke of excellent quality, therefore, the use of excellent coking coal is necessary. The large-sized blast furnaces which have been developed recently for increasing the yield of iron require a large amount of excellent quality coke and thus, there is a demand for a large amount of coal suitable for producing metallurgical coke, particularly for strongly-coking coal. However, many parts of the world are not possessed of an abundant quantity of such strongly-coking coal, and because of this and shipping costs, the price of that coal has become higher and higher. Accordingly, it has become difficult to maintain both the strength and the price of the coke at levels of the past.
In order to solve this problem, several investigations have been performed according to which lower-grade-coal is changed into higher-grade-coal, and in this manner the strength of coke is kept at previous levels. For example, the following processes have been investigated:
a process of manufacturing formed-coke by hot briquetting; PA1 a process of feeding molding-coal into a chamber oven; PA1 a process of feeding dryed-coal into a chamber oven; and PA1 a process of manufacturing reformed coal by blending petroleum-pitch.
However, because all of the processes described above possess one or more unresolved technical and/or economical problems, the manufacturing industry has not yet adopted any of them, and therefore there has not been a sufficient reduction in the use of higher-grade-coking coal. Furthermore, since the sulphur content in the lower-grade-coal is not reduced in accordance with the proposed processes, the coke produced from coal produced thereby has inferior properties.
There is in the world a large amount of coal with higher strength as an aggregate and lower coking capacity. When a suitable binder is blended with coal of this type, excellent coke for iron manufacturing is produced. Accordingly, provision of a binder which has suitable coking properties is necessary from the stand-point of conserving natural resources and improving the economy.
Coal pitch, petroleum pitch, reformed asphalt or "Bojuntan" have previously been considered as binders. Desirable properties of a binder require that the binder melts at a temperature of between about 400.degree. C.-500.degree. C. to a plastified state and causes coal particles to adhere to each other. Also, because of the reasons set forth above, it is necessary that a binder has a structure similar to the coking component of coal, which is composed of condensed, aromatic ring structures. On the basis of these considerations, various manufacturing methods for the binder have been attempted to produce a substance for blending with raw coal, but such a product providing a sufficient effect has yet to be produced.
Generally, since coal mainly has the structure of condensed, aromatic ring structures, a satisfactory binder can be produced from coal by a method wherein side chains and functional groups in coal are reduced, the bonds between each aromatic rings are broken, and only the portion of condensed, aromatic substances is separated and extracted.
On the basis of these considerations, the method of "Bojuntan" was tried. But, by this method, since the coal is thermally treated only at normal pressures, the fundamental structure of the coal is not changed and the particles of coal are only swelled by the large quantity of solvent. For this reason, in order to produce an excellent binder by this method, careful selection of the coal is necessary. Furthermore, productivity is low and the sulphur content, which is harmful for coke, is not reduced by this method.